Field
Embodiments of the present disclosure relate to systems and methods for wirelessly monitoring well conditions using a power generator that generates power based on friction, generated by fluid or mud flow, between two materials of opposite polarity.
Description of Related Art
Background
Surveying and logging tools used in downhole environments consist of a Measurement While Drilling (MWD) tool and several Logging While Drilling (LWD) tools. The basic MWD tool measures wellbore parameters such as tool face orientation, inclination, azimuth, as well as environmental data such as internal temperature, tool vibration. Some dedicated near bit tools provide measurements of additional drilling parameters such as weight on bit (WOB), bit torque, etc. Typical LWD tools measure formation parameters such as gamma ray, neutron density/porosity, resistivity and nuclear magnetic resonance. The LWD tools come in combo packages, where the drilling engineer has the option of choosing the LWD tools required for a given well section.
The data from LWD and MWD sensors are transmitted to the surface using a technique called mud pulse telemetry. Mud pulse telemetry utilizes changes in mud flow pressure or pressure waves to transmit data from the tool to the surface. The three main mud pulse telemetry methods are positive, negative and continuous pulse systems. In positive pulse telemetry, the flow of mud is blocked and unblocked for short times with a valve so that the pressure inside the drill string increases and then returns to its original state, respectively. In negative pulse telemetry a dump valve is opened to divert mud from inside the drill string to the annulus resulting in the reduction of pressure in the drill string. When the valve is closed the pressure returns to its original state. In a continuous pulse system a stator and a rotor system, which can be shifted against each other, restricts the mud flow in way to produce continuous positive pressure pulses.
Typically accurate survey data is acquired during a static condition when making a pipe connection and mud pulse telemetry is activated by a pre-programmed mechanism such as mud flow or mud pressure increase within the tool. The mud pulse system then sends corresponding pressure pulses to the surface. These pressure pulses are converted to comprehensible data by pressure transducers and signal processing. This process is an example of ‘uplink’ communication. While mud pulse telemetry is the most widely used and reliable method of downhole communication, data communication through mud is slow and mud pulse can only reach speeds up to 20 bits per second. It should be noted that mud pulse telemetry does not work well when pressure waves are attenuated significantly due to multiphase fluids in the drillstring.
There are also other methods that can be used such as running wire cables along the drill string, which is faster than mud pulse telemetry. However, this is an expensive procedure and is not feasible due to reliability issues. Running a large number of wires with many electrical connectors through a drill string in a liquid environment gives rise to many reliability issues that can only be resolved by pulling the drill string out of the hole. Electromagnetic waves are another method to transfer data from downhole to the surface but they experience significant attenuation and decay in downhole formations and liquids. Therefore, the frequencies used are very low resulting in a data rate similar to mud pulse telemetry. Similarly acoustic waves can be used to transmit data but the noise generated in a drilling environment has a significant influence on the sensitivity resulting in a low signal-to-noise ratio.
In onshore wells the MWD/LWD tools are typically used in directional drilling but in offshore wells generally only MWD tools are used. The method of communication between MWD/LWD sensors downhole and the surface is an integral component of MWD/LWD systems. The current method of communication, mud pulse telemetry, is very slow, has low resolution and haven't progressed at the same rate as the MWD/LWD sensors. With the advent of new technologies that can measure downhole parameters with increased resolution and sensitivity there is a need for faster data transmission. Thus a faster data communication method than mud pulse telemetry is needed to fully utilize the higher resolution data that advanced sensors can obtain.